A telescope buried in Antarctic ice has returned its first results, proving that it can successfully detect elusive, invisible particles called neutrinos. The astronomer in charge of the project said that while the initial neutrino map of the sky is preliminary, it provides tantalizing hints of powerful "cosmic accelerators."
The map, unveiled for astronomers in Australia this week at a meeting of the International Astronomical Union, provides the first observational glimpse of very high energy neutrinos, ghostly particles that are believed to emanate from some of the most violent events in the universe.
Neutrino sources are thought to include colliding black holes and the violent cores of distant, young galaxies.
(Antarctic Muon and Neutrino Detector Array). It was built with support from the National Science Foundation (NSF) and is composed of arrays of light-gathering detectors buried in ice 1.5 kilometers beneath the South Pole. Because cosmic neutrinos are invisible, uncharged and have almost no mass, they are next to impossible to detect, Halzen and his colleagues said in a statement. Unlike photons, the particles that make up visible light, and other kinds of radiation, neutrinos can pass unimpeded through planets, stars, the vast magnetic fields of interstellar space, and even entire galaxies. That quality -- which makes them very hard to detect -- is also their greatest asset as the information they harbor about cosmologically distant and otherwise unobservable events remains intact.
Studying neutrinos is a slow process.
The map produced by AMANDA II is preliminary, Halzen emphasized. It represents a year of data-gathering. Using two more years of data already harvested with AMANDA II, Halzen and his colleagues will next define the structure of the sky map and sort out potential signals from statistical fluctuations.
The significance of the map, according to Halzen, is that it proves the detector works.
Neutrinos can penetrate the Earth. So the telescope is designed to look down into the Antarctic ice. AMANDA II looks through the Earth to the sky in the Northern Hemisphere.
The telescope consists of 677 glass optical modules, each the size of a bowling ball, arrayed on 19 cables set deep in the ice with the help of high-pressure hot water drills. The array transforms a cylinder of ice 500 meters in height and 120 meters in diameter into a particle detector.
The glass modules work like light bulbs in reverse. They detect and capture faint and fleeting streaks of light created when, on occasion, neutrinos crash into ice atoms inside or near the detector. The subatomic wrecks create muons, another species of subatomic particle that, conveniently, leaves an ephemeral wake of blue light in the deep Antarctic ice.
The streak of light matches the path of the neutrino and points back to its point of origin.
The fact that AMANDA II has now identified neutrinos up to one hundred times the energy of the particles produced by the most powerful earthbound accelerators raises the prospect that some of them may be kick-started on their long journeys by some of the most supremely energetic events in the cosmos. The ability to routinely detect high-energy neutrinos will provide astronomers not only with a lens to study such bizarre phenomena as colliding black holes, but with a means to gain direct access to unedited information from events that occurred hundreds of millions or billions of light years away and eons ago.
"This map could hold the first evidence of a cosmic accelerator," Halzen said. "But we are not there yet."
Plans call for AMANDA II to get new strings of detectors and to grow to a cubic kilometer of instrumented ice. The new telescope, to be known as IceCube, should make scouring the skies for cosmic neutrino sources highly efficient
"We will be sensitive to the most pessimistic theoretical predictions," Halzen said.
Another neutrino telescope, called
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